1. Field of the Invention
The present invention relates to physiological monitoring.
2. Discussion of the Background
Atrial Fibrillation (AF) is a common cardiac arrhythmia that is estimated to affect at least 2.2 million patients in the United States. Patients suffering from AF have a two to seven times higher risk of stroke, and the disease has been reported to account for approximately fifteen percent of all strokes that occur nationally. Currently, there exist a variety of treatments for AF. These include rate or rhythm control medications, cardioversion, and the catheter ablation of arrhythmogenic regions inside the heart.
The human heart normally beats between sixty to one-hundred beats per minute when a person is at rest. In AF, the heart's electrical signals do not travel through normal pathways, but instead spread throughout the atria in a rapid and disorganized fashion, which in turn can cause the atria to activate in a chaotic fashion.
The onset of cardiac arrhythmia may be accompanied by physical symptoms. For instance, common symptoms in AF patients may include palpitations, an irregular fluttering sensation in the patient's chest, shortness of breath, dizziness, or a sudden feeling of weakness. Nevertheless, it is also common for physical symptoms to be absent during the onset of certain arrhythmic episodes, and in such cases, these asymptomatic cardiac arrhythmias, though serious, may go unnoticed by the patients.
One of the difficulties associated with the follow-up of AF treatment procedures lies in accurately assessing the long-term burden of AF in patients. Long-term (i.e. greater than 1 month) follow-up of a patient's cardiac rhythm is crucial for the optimal management of AF patients, with regard to the assessment of treatment efficacy and to the potential discontinuation of anticoagulation therapy. Currently, physicians do not have any means of gathering detailed information over an extended period of time regarding the true burden of AF in patients that will enable them to accurately determine the success of a treatment procedure in patients.
Known monitoring devices have not been able to fully address this problem of long term and continuous cardiac monitoring. One such approach to this problem involves the use of a “cardiac event monitor.” This solution includes the use of a portable electrocardiography (ECG) recording device that is carried by the patient and communicates with one or more wired electrodes that are worn under the patient's clothing, and are adhesively attached to the patient's skin. The device records the heart's electrical activity at the push of a button. Patients trigger the device when they first begin to feel signs or the onset of physical symptoms that signal an “event”, such as dizziness, weakness, palpitations or lightheadedness. The device is also capable of storing the patient's cardiac rhythm by recording a rolling “window” of ECG data, which can later be transmitted over phone lines for review by a qualified physician. One example of a cardiac event monitor is described in U.S. Pat. No. 7,117,031.
Unfortunately, the cardiac event monitor does not adequately address the need for long-term and continuous monitoring of a patient's cardiac rhythm during follow-up of a treatment. Current cardiac event monitors can only be worn for up to a period of thirty days, and removal of the device is required during certain patient activities such as swimming or bathing. This in turn renders the device as not being truly continuous in its monitoring of cardiac arrhythmia events. Second, because patients may undergo asymptomatic recurrences of their arrhythmia, the reliance of the event monitor on detecting only symptomatic episodes in patients (i.e., symptom triggered recordings) can result in inaccuracies during determination of the true effectiveness of a treatment.
Furthermore, it is often cumbersome for the patient to have to be constantly connected to a set of wires and chest electrodes throughout the day, and the device can be difficult for many patients to integrate into their active lifestyle. Finally, the continuous attachment of sticky electrodes to the patient's chest tends to cause skin irritation, which further exacerbates the issue of poor patient compliance.